Spinal fixation devices are used to stabilize surgically fused vertebrae. Conventional devices consist of an assembly generally made up of titanium bone screws, reinforcing rods, and other components. A certain level of complexity exists in installing spinal fixation devices in that the implementor has to twist as many as two dozen threaded fasteners onto respective bone screws and/or bone hooks.
Threadings, in the context of spinal fixation devices, provide a variety of fundamental problems during installation. Since""spinal devices generally need to be assembled through an incision, it can be difficult to catch the first thread amongst the surrounding soft tissue, blood, and other fluids. Additionally, some screws installed in an incision environment can too easily suffer from cross-threading.
As another shortcoming of conventional spinal fixation devices, threadings on screws and nuts allow for inconsistent tightening during installation. The installation of apparatuses which include threadings allow for different implementors to apply a wide range of torque levels, some in excess of the desired amount, thus increasing the chance of surgical slips during installation, as well as equipment failure.
Further, it is well known that prolonging the time of surgery both increases the patient""s risk of infection as well as complications associated with anesthesia. The use of threaded screws and nuts can consume significant amounts of surgical time that ideally would be avoided.
Additionally, threaded fasteners are problematic in that such traditional set screws can work their way loose when confronted with continuous micro-motion of the spine.
As yet another shortcoming of some conventional spinal fixation devices, fasteners are fastened to the interior surface of respective channeled hooks and/or screws to immobilize rods positioned in such channels. While using a fastener that fits into the screw and/or hook may be desirable for the sake of saving space, such a design does allow for the possibility of channels widening over time until the device fails.
A need exists for a spinal fixation device, and corresponding fastener of such device, that can be assembled in an improved amount of time, with less chance of inaccuracies, and with greater reliability than conventional methods.
It is therefore an object of this invention to provide a spinal fixation device, for use in the incision environment, which lacks complex assembly steps.
It is another object of this invention to provide a spinal fixation device in which substantially uniform torque is required to assemble such spinal fixation device.
It is yet another object of this invention to provide a spinal fixation device which enables an installer to affix the device to a recipient with greater time-efficiency than conventional methods.
It is still another object of this invention to provide a spinal fixation device which does not loosen due to mechanical failure of the device or normal micro-motions of the vertebrae.
In a first family of embodiments, the invention comprehends a spinal fixation device for use with an elongate brace member. The spinal fixation device comprises an attachment component, a seat, a seat fastener, and a saddle. The attachment component functions to secure the spinal fixation device to a desired bone structure. The seat comprises an inner seat surface and an outer seat surface. The seat has a brace canal along the inner seat surface for positioning of the brace member, and the outer seat surface has a locking channel. The seat fastener has a top, a bottom, an outer side surface, and an inner side surface; the inner side surface includes a lip. The saddle is disposed between the brace member and the seat fastener. The locking channel of the seat is designed and configured to form a cooperative engagement with the lip of the seat fastener, thereby enabling the lip of the seat fastener to lockingly engage the locking channel of the seat. The brace member is compressively loaded into a cooperation with the seat and the saddle by compression resulting from tightening of the seat fastener to the seat so as to lock the relative position between the seat and the bone attachment component.
In preferred embodiments, the saddle is adapted to bear upon the elongate brace member, upon tightening of the seat fastener, thereby to compress the elongate brace member into a secure engagement with the brace canal of the seat.
In most embodiments, the attachment component is a threaded screw portion, a lamina hook, or a pedicle hook.
Preferably, the cooperative engagement between the lip of the seat fastener and the locking channel of the seat is a high friction interface.
In some embodiments, the lip of the seat fastener further comprises a lock-notch, and the locking channel of the seat further comprises a complimentary lock-groove, whereby, upon sufficient tightening, the lock-notch interfaces with the lock-groove, thereby further securing the cooperative engagement between the lip of the seat fastener and the locking channel of the seat.
In other embodiments, the lip of the seat fastener further comprises a lock-groove, and the locking channel of the seat further comprises a complimentary lock-notch, whereby, upon sufficient tightening, the lock-notch interfaces with the lock-groove, thereby further securing the cooperative engagement between the lip of the seat fastener and the locking channel of the seat.
In preferred embodiments, the cooperative engagement between the lip of the seat fastener and the locking channel of the seat is achieved by turning the seat fastener approximately 90 degrees.
The spinal fixation device is generally one or both anodized and made of titanium.
In preferred embodiments, the lip tapers about 0.04 inch to about 0.05 inch over a 180 degree arc.
In some embodiments, the seat and the seat fastener both have visual orientation indicators which come into alignment upon tightening the seat fastener to the seat by cooperatively engaging the lip of the seat fastener and the locking channel of the seat, and turning the seat fastener approximately 90 degrees.
In a second family of embodiments, the invention comprehends a spinal fixation device for use with an elongate brace member. In such embodiments, the outer seat surface of the seat has a lip, and the inner side surface of the seat fastener includes a locking channel. Accordingly, the locking channel of the seat fastener is designed and configured to form a cooperative engagement with the lip of the seat, thereby enabling the lip of the seat to lockingly engage the locking channel of the seat fastener. The brace member is compressively loaded into a cooperation with the seat and the saddle by compression resulting from tightening of the seat fastener to the seat so as to lock the relative position between the seat and the bone attachment component.
In preferred embodiments, the cooperative engagement between the lip of the seat and the locking channel of the seat fastener is a high friction interface.
In some embodiments, the lip of the seat further comprises a lock-notch, and the locking channel of the seat fastener further comprises a complimentary lock-groove, whereby, upon sufficient tightening, the lock-notch interfaces with the lock-groove, thereby further securing the cooperative engagement between the lip of the seat and the locking channel of the seat fastener.
In other embodiments, the lip of the seat further comprises a lock-groove, and the locking channel of the seat fastener further comprises a complimentary lock-notch, whereby, upon sufficient tightening, the lock-notch interfaces with the lock-groove, thereby further securing the cooperative engagement between the lip of the seat and the locking channel of the seat fastener.
Preferably, the cooperative engagement between the lip of the seat and the locking channel of the seat fastener is achieved by turning the seat fastener approximately 90 degrees.
In some embodiments, the seat and the seat fastener both have visual orientation indicators which align upon tightening the seat fastener to the seat by cooperatively engaging the lip of the seat and the locking channel of the seat fastener, and turning the seat fastener approximately 90 degrees.